Inductorless forward-flyback soft-switching converter with dual constant on-time modulation for photovoltaic applications

A family of inductorless forward-flyback converters utilizing dual constant on-time modulation is proposed, in order to maintain high efficiency over a wide load and input range. The main switch is turned on for the constant half resonant period to achieve zero-current-switching for the forward diode and to minimize the deadtime between the two output diodes. The auxiliary active switch is in the on-state with a very short constant interval to realize zero-voltage-switching for the main active switch, even if the magnetizing inductor operates in the continuous current mode. Experimental results for a 250 W hardware prototype verifies soft-switching operation from zero to full load over 25 to 45 V input range and the CEC weighted efficiency reaches 97%. The proposed converter is attractive for the tree-type PV system applications.